Insecticide resistance status of Aedes aegypti in Bangladesh

Arboviral diseases including dengue and chikungunya are a major public health concern in Bangladesh, with unprecedented levels of transmission reported in recent years. The primary approach to control these diseases is control of Aedes aegypti using pyrethroid insecticides. Although chemical control is long-practiced, no comprehensive analysis of Ae. aegypti susceptibility to insecticides has previously been conducted. This study aimed to determine the insecticide resistance status of Ae. aegypti in Bangladesh and investigate the role of detoxification enzymes and altered target site sensitivity as resistance mechanisms. Aedes eggs were collected using ovitraps from five districts across the country and in eight neighborhoods of the capital city Dhaka from August to November 2017. CDC bottle bioassays were conducted for permethrin, deltamethrin, malathion, and bendiocarb using 3-5-day old F0-F2 non-blood fed female mosquitoes. Biochemical assays were conducted to detect metabolic resistance mechanisms and real-time PCR was performed to determine the frequencies of the knockdown resistance (kdr) mutations Gly1016, Cys1534, and Leu410. High levels of resistance to permethrin were detected in all Ae. aegypti populations, with mortality ranging from 0 - 14.8% at the diagnostic dose. Substantial resistance continued to be detected against higher (2X) doses of permethrin (5.1 - 44.4% mortality). Susceptibility to deltamethrin and malathion varied between populations while complete susceptibility to bendiocarb was observed in all populations. Significantly higher levels of esterase and oxidase activity were detected in most of the test populations as compared to the susceptible reference Rockefeller strain. A significant association was detected between permethrin resistance and the presence of Gly1016 and Cys1534 homozygotes. The frequency of kdr alleles varied across the Dhaka populations, and Leu410 was not detected in any of the tested populations. The detection of widespread pyrethroid resistance and multiple mechanisms highlights the urgency for implementing alternate Ae. aegypti control strategies. In addition, implementing routine monitoring of insecticide resistance in Ae. aegypti in Bangladesh will lead to a greater understanding of susceptibility trends over space and time, thereby enabling the development of improved control strategies. Author summaryGlobally, arboviral diseases including dengue, chikungunya, and Zika are major public health problems. Bangladesh recently experienced its two worst outbreaks of chikungunya and dengue, involving hundreds of thousands of people. The principal vector of these diseases, the Aedes aegypti mosquito, is present throughout Bangladesh, especially in the major cities including the capital, Dhaka. The control of Ae. aegypti in Bangladesh has long been based on space sprays by thermal fogging of pyrethroid insecticides. However, no comprehensive assessment has previously been conducted to understand the insecticide resistance status of Ae. aegypti. We tested Ae. aegypti collected from places of historical arboviral outbreaks to determine their insecticide resistance status, as well as some of the underlying mechanisms causing the resistance. All of the populations tested were highly resistant to permethrin, the key insecticide used by vector control programs in Dhaka, with varying degrees of resistance to deltamethrin and malathion, and full susceptibility to bendiocarb. High levels of esterase and oxidase enzyme activity and the presence of mutations on the voltage-gated sodium channel gene were detected as key mechanisms underpinning the resistance. The findings of this study provide the first comprehensive evidence base for improving Ae. aegypti control strategies in Bangladesh.